(I) Chemical reaction
[Ca3(PO4)2]3.CaF2+7H2SO4(aq)--------> 3CaH4(PO4)2.7CaSO4+2HF
(¡¡) Raw Materials
A high grade (30-35% P2O5) of natural or benificiated phosphate rock is ordinarily specified, since the demand is for high P2O5 content product. Dilute sulphuric acid (62-70%) is the only other Chemical involved.
(¡¡¡)Basis- 1 ton of superphosphate
Phosphate rock 0.5-0.6 ton
Sulphuric acid 0.3-0.4 ton
Plant capacity 100-1400 tons/day
(¡v) Process description
Phosphate rock lumps are crushed in jaw crusher and ground to -100 mesh in a hammer or ring mill. A continuous feed of dilute sulphuric acid and powdered rock phosphate is monitored by automatic control into a steel truogh, lead lined and brick lined , covered with a hood to collect SiF4 and HF fumes. The rotating mechanism made of cast iron blades on a square shaft, moves the product gradually forward at the rate of 0.2 to 0.5 m/min through the 12-15 meter reactor conveyor unit. With proper grinding and acid control, the reaction is effectively complete and can be sent directly to the granulator. The older method was to store for a nominal 24 hour period to insure complete reaction.
The SiF4 and HF fumes along with CO2 are scrubbed in water and the silica is removed by NaCl according to chemical equation.
The porous, crumbly material from the den is mixed with rock dust from the grinding sections of the plant and fed to the inside of a sloping rotary drum. Water is sprayed on the tumbeling solids to form free flowing granules and to enhance the acidulation reaction. Product is dried in a rotary dryer and packaged in 50 kg plastic lined juite bags.